1. Field of the Invention
The invention relates generally to methods and apparatus for applying coatings. In particular, the invention relates to rotary atomizers which atomize material to be applied as a coating. Further, in particular, the invention relates to a rotary atomizer which reduces or eliminates the need for external shaping air to direct atomized material to an object to be coated. The coating material can be, for example, a liquid or powder.
2. Related Art
The use of rotary spray atomizers to apply coatings to an object is well known. One such application of rotary spray atomizers to coat objects is the application of paint and other coatings to newly manufactured automobiles.
FIG. 1 herein illustrates a conventional rotary atomizer, such as bell cup 101 attached to turbine 103. Such rotary atomizers typically have a smooth exterior surface. Typically, a shaft in the turbine (not shown) causes the bell cup to rotate at a desired speed. Material to be atomized, such as paint, is supplied to the bell cup as it rotates. The paint or other material to be atomized travels along the interior of the bell cup and exits the bell cup 101 through a single opening or a plurality of openings 105 on the face of bell cup. In order to control the shape of the distribution of atomized material, shaping air is transmitted through outlets 107 of turbine 103. The shaping air is typically supplied from an independent source to achieve the fan shaped pattern of atomized product distribution shown generally at 109 in FIG. 1. Essentially, the shaping air directs the atomized material outward and away from the bell cup 101 to prevent too wide a distribution of the material as shown by dotted lines 111. One characteristic of this type rotary atomizer is the presence of a "pancake" of atomized material 113. The pancake of atomized material creates imperfections in the application of the atomized material as a coating, such as in painting applications.
Notwithstanding the use of independent shaping air to direct atomized materials such as paint away from bell cup 101, "blow back" of such material is always a problem. Various apparatus such as a shaping air plate or a shaping air shroud have been used to reduce blow back. However, when external shaping air is used, some of the atomized coating material inevitably travels behind the rotary atomizer or bell cup thereby coating the rotary atomizer, the turbine housing and any other robotic components attached to them. The blow back of coating material onto the rotary atomizer bell cup, turbine housing and other components results in increased maintenance, since such components require constant cleaning. In addition, blow back of coating material toward the turbine decreases the life expectancy of the turbine and lowers coating efficiency and performance.